Spark-ignition engines typically operate by introducing a stoichiometric mixture of air and fuel into a cylinder of an engine. A piston then compresses this mixture, and at a predetermined crankshaft angle, a spark plug will ignite the air/fuel mixture producing a flame front that propagates through the combustion chamber. The rapid increase in heat from the burned fuel triggers an increase in pressure which forces the piston downward in the cylinder. The ability to precisely time the combustion event through the use of a spark plug is a benefit of the spark-ignition engine. However, the spark-ignition engine may be somewhat inefficient since the compression ratio of the engine is kept to a relatively low level to avoid “knock.” Knock occurs when the air/fuel mixture ignites independently of the spark plug and may cause engine damage.
Another condition affecting engine operation involves misfire occurrences. For engines operating with one or more cylinders that are EGR cylinders, a misfire in the EGR cylinder(s) impacts the performance of the other cylinders due to the recirculation of the output from the EGR cylinder. For example, in a misfire condition an additional amount of hydrocarbons from the EGR cylinders is passed back to the intake of the other cylinders. This additional fuelling in combination with the misfire condition can result in catalyst damage and increased emissions.
Engines with one or more cylinders that provide primary or dedicated EGR flow can enjoy greatly simplified controls and pressure management, fewer hardware devices, and other benefits. However, these simplifications come at the cost of a loss of control over the system, including a loss of control due to the different conditions that may be present in the EGR cylinder(s) compared to the other cylinders, such as characteristics of the charge flow, fuel, exhaust, and combustion associated with the EGR cylinder(s). An engine having primary EGR cylinder(s) provides an opportunity for greater control over the temperature and composition of the charge flow to the intake manifold, if a system could be developed to take advantage of this opportunity. Therefore, further technological developments are desirable in this area.